Method of purification of filtering agent



Feb, 17, 1925. 1,526,520

P. A. BQEcK ET Al.

IETHOD OF PURIFICATION OF FILTERING AGENT Filed Dec. 27, 1920 Wafer J'lveehrdfer 7l/dye fo Process INVENTORS Perc/ 4. 50er/f BY Har/y .5f Tmc/ver ATTORNEY.

Patented Feb. 17, 17925.v

UNITED STATES PATENT OF FICE PERCY A. BDECK AND HARRY S. rTHATGEIIllEt, 0F LOS ANGELES, CALIFORNIA, AS-

SIGNORS, BY MESNE ASSIGNMENTS, T0 THE CELITE COMPANY,

DELAWARE.

A CORlPORATION 0F METHOD 0F PURIFICATION 0F FILTER/ING- AGENT.

Application led December 27, 1920. Serial No. 433,279.

To all whom t may concern.'

Be it known that-we, PERCY A. Benoitand HARRY S. THATCHER, citizens of the United States,v residing at Los Angeles, in fthe county of Los Angeles and State of California, have invented a new and useful Method of Purification of Filtering Agent, of which the following is a specification.

This invention relates to purification of filtering agents and primarily to the recovery and re-use of the residue from sugar filtration, or from the filtration of other liquids containing suspended impurities. in the manufacture and refining of sugar it is usual to employ a filtering agent to render more effective the ltration in lilter presses, or otherwise, of the sugar liquor or v colloidal or slimy nature, land it has been found that filtration can be much more effectively carried on when a filtering agent,"

such as diatomaceous earth, is added to the liquid or used in conjunction with the ltering operation, such filtering agent having the function of maintaining the filter bed or cake in a more open and permeable condition and also of absorbing more or less of the impurities. In the use of this filtering agent in a filter press, for example, the agent accumulates along with the solid impurities in the filter cake and in cleaning the filter the Vfiltering agent used forms part of the sludge removed from the filter and has generally been discarded as unfit for further use. This invention relates tothe treatment of such sludge for the recovery of the diatomaceous earth, or filtering agent, with a view to its re-use in the process, either in a similar, or another filtering operation.

The term filtering agent as herein used is intended to include not only diatomaceous earth but other inorganic materials having somewhat similar fproperties, for example, certain varieties o asbestos, such as short fibre asbestos.

rihe accompanying drawing is a ow sheet showing one manner of carrying out the invention in refining of raw cane sugar. l

Referring to the drawing the raw sugar is washed 1n a centrifugal, indicated at 1, and the washed raw sugar thenpasses to the melting pan, indicated at 2, where it is brought into solution with water supplied from any suitable source, including, for example, sweet water obtained in any stage of the refining process or ltrate from one or more of the filtering operations hereinafter referred to. The raw sugar solution or liquor passes to the blow-up 3 wherein 1t is mixed by air agitation, or otherwise, with the ltering agent (diatomaceous earth) and is then forced by pump 4, or by gravity, to the filter press 5. The filtrate from this lter press` passes to the usual subsequent steps of the refining process, including further purification, decolorization, evaporation and crystallization. The sludge from the liltcr press 5 is sluiced or washed therefrom with water in usual manner and passes to a separating means for separating, as far as practicable or desirable, the solid constituents of the sludge from the liquid or solution constituents thereof. For this purpose it is preferred to use continuous settling tanks, such, for example, as Dorr thickeners, as described and illustrated -on pages 332-4 of Principles of Chemical Engineering by Walker, Lewis and Mc- Adams, published 1923 by McGraw-Hill Book Company, indicated at 16 and 20, in which the coarser solid constituents of the sludge, including a large proportion of the filtering agent used, "is separated from the liquid the operation of the two settling tanks serving to first separate the heavy solids and then the coarser parts of the filter agent, which passes ofi at an outlet, indicated at 7. When diatomaceous earth is used as a filtering agent the solid material so withdrawn at the outlet 7 consists mainly or largely of that Aportion of the diato maceous earth, or filtering agent, which is dition as distinguished from the finer particles of diatomaceous earth, or filtering agent, which tend to remain suspended in the liquid and to pass off with the slimes and clay and impurities, gums, fibre, cellulose, etc. from the settling tanks 16 and 20. This coarser diatomaceous earth is more especially adapted for filtration tered through the diatomaceous. earth in the first filtering operation above described.

VThese Washings contain, in particular, a

higher proportion of gummy, colloidal, slimy impurities and are therefore much more difficult to filter than the raw sugar liquor. We therefore prefer to use the diatomaceous earth recovered as above, which is relatively free from fine `material and therefore especially well fitted for use as a filter-aid, in the filtration of this more diflater stages of the refining process along.

or separately from the filtrate from the filter press 5.. ,The sludge from the washings filter press 10 may pass, as indicated, back to the continuous settling tanks for cyclic operation for recovering and reusing the filtering agent from such sludge. It will be understood, however, that inasmuch as new filtering agent is continually being added, as may be required, (at blow-up 3) in the treatment of the raw `liquor an equivalent amount of filtering agent must be Withdrawn from the cycle, either continuously or from time to time. For this purpose a certain proportion .of the sludge from the filter press 10 may pass, if desirable, to Waste or be discarded, as indicated. A certain amount of the filterin agent is also lost to the cycle at the overow from settling tanks 16 and 20. 1f found desirable, a portion of the recovered filtering agent from the settling tank 6 may be passed to the blow-up 3 for use in the primary filtration of the raw' sugar solution.

The overflow from the continuous set` tling tank 20 generally contains, in .addit1on to more or less sugar solution, a certain amount of solid impurities which are largely of a colloidal, nature, including, however, more or less of the filtering agent, especially that portion of the rfiltering agent which is in extremely finely divided condition and tendsl to remain suspended in the liquid. ln son'e cases the amount and condition of the filtering agent so present is tering agent, especially that portion thereof which is in a condition of extremely fine division, will pass to waste at this point along with the slimy material, and in some cases the process may be so carried out that the waste or loss of' filtering agent is confined to this point, all of the filtering agent fromthe filter press 10 being in this case .retained in the cycle by being returned to settling tanks.

By the above described operation it is possible to re-use amajor portion, or at leasta considerable portion of the ltering agent which has been employed in the filtering operation so that the working capacity or effective life of a given amount of filtering agent is considerably increased.

llt is desirable to carr out 'the separating action for removing ltering agent from the other constituents of the sludge in a plurality of operations, for example, as shown in the drawing, the sludge may pass from the lter press 5 to a continuous settling tank 16 for settling out the coarse mud or heavy solids leaving the bulk of the filtering agent, which is comparatively light, in suspension in a rapid stream of the liquid. An overflow, indicated at 18, carries 0E liquid containing filtering agent in considerable portion to the second continuous settling tank 20 wherein the sludge containing a considerable portion of the filtering agent settles out and is utilized. for filtration, as above described. The overfiow from the tank 20 may pass to the filter press 14, as above described, together with the lighter or more finely divided portion of the filtering agent. 1t may be desirable to furnish additional filtering agent in the filter press 14 to supplement the action of the filtering agent carried over in the overflow from the tank 20 and this may be carried out, as indicated, by conducting a portion of the liquor pumped from the blowup 8 to the filter press7 14 and another portion of such liquor to the filter press 10.- In case it is'found desirable to remove from the cycle some of the slimes before the liquor passes to the last settlin tank 20 this may be effected, as indicate by conduct' ing such slimes from an overfiow 23 and placing the overflow 18 at an intermediate point in the settling tank between the outlet 17 and the overflow 23, so-that the liquor passing ofi at 18 will be comparatively free from the extremely colloidal slimes passing oi at 23 and also from the heavy solids ing diatomaceous earth used as a filter-aid -passin olf at 17. in su ar refining, which consists in subject- Whi e our process has been described ing 51e filter-cake mixed with water to a 15 with especial reference to the residue from settling voperation to separate the liquid 5 sugariiltration, itis also applicable to reinto three portions containing respectivel covery of diatomaceous earth used as filterslime, diatomaceous earth, and heavy so ing agent from filtration residue provided ids, and subjecting the diatomaceous earth in the'treatment ofother organic solutions containing liquid to a further separating 2U containingrsuspended material, for example, operation to recover the diatomaceous earth l0 fruit juices of any kind. l for reuse.

. What we claim is: PERCY A. BOECK.

A process of treating filter-cake contain- HARRY S. THATCHER. 

